Surface electrodes are employed in medical procedures for sensing electrical and/or magnetic fields used in tracking the location of medical devices within a patient's body. In cardiac mapping systems, such surface electrodes may be used for tracking the location of catheters, introducers, probes, and/or other medical devices inserted into the body. In the ENSITE PRECISION™ cardiac mapping system available from St. Jude Medical, Inc., for example, such surface electrodes may be used as part of a localization system that tracks the location of device(s) inserted into the body using electric and magnetic fields.